The present invention pertains to a method for preparing the transition metal component of a Ziegler-Natta catalyst which method provides a means for varying the average particle size and particle size distribution of .alpha.-olefin polymers produced in the presence of said catalysts.
U.S. Pat. No. 4,526,943 issued July 2, 1985 to Fuentes, Jr. et al and U.S. Pat. No. 4,544,647 issued Oct. 1, 1985 to Fuentes, Jr. et al disclose a Ziegler-Natta catalyst useful in the polymerization of one or more .alpha.-olefins. While these catalysts are very efficient, no method for controlling the average particle size or particle size distribution was provided. In some instances such as when an .alpha.-olefin polymer is to be chemically modified while still in the powder form, it is desirable to have as small an average particle size as possible in order to present a large surface area for modification. Also when chemical modification of the .alpha.-olefin polymer is desired, a narrow particle size distribution provides for a more uniformly reacted .alpha.-olefin polymer. It is also sometimes desirable to have a small average particle size when efficient removal of the inert polymerization diluent from the .alpha.-olefin polymer is required. In some instances in which extrusion processing of the polymer is not performed, it is desirable to have as large an average particle size as possible and a narrow particle size distribution for improved handling of the .alpha.-olefin polymer.
The present invention provides a method for preparing the transition metal component of a Ziegler-Natta catalyst which permits the preparation of .alpha.-olefin polymers having a relatively small average particle size and with a narrow particle size distribution while maintaining a high catalyst efficiency.